Reionization after JWST: a photon budget crisis?

Reionization after JWST: a photon budget crisis?

12 April 2024 | Julian B. Muñoz, Jordan Mirocha, John Chisholm, Steven R. Furlanetto, and Charlotte Mason
The James Webb Space Telescope (JWST) has revealed that early, faint galaxies are prolific producers of ionizing photons, which challenges the consensus that star-forming galaxies can drive reionization. The new observations infer high ionizing efficiencies ($\xi_{\text{ion}}$) and an enhanced abundance of early galaxies, leading to an excess of ionizing photons. This excess, combined with low-$z$ studies predicting significant escape fractions for faint reionization-era galaxies, results in reionization ending too early. The current galaxy observations, taken at face value, imply a photon budget crisis that tensions with cosmic microwave background (CMB) and Lyman-$\alpha$ forest data. To resolve this crisis, possible solutions include missing astrophysical or observational selection effects, as well as enhanced recombinations. Further observations of both galaxies and CMB are needed to understand the reionization process better.The James Webb Space Telescope (JWST) has revealed that early, faint galaxies are prolific producers of ionizing photons, which challenges the consensus that star-forming galaxies can drive reionization. The new observations infer high ionizing efficiencies ($\xi_{\text{ion}}$) and an enhanced abundance of early galaxies, leading to an excess of ionizing photons. This excess, combined with low-$z$ studies predicting significant escape fractions for faint reionization-era galaxies, results in reionization ending too early. The current galaxy observations, taken at face value, imply a photon budget crisis that tensions with cosmic microwave background (CMB) and Lyman-$\alpha$ forest data. To resolve this crisis, possible solutions include missing astrophysical or observational selection effects, as well as enhanced recombinations. Further observations of both galaxies and CMB are needed to understand the reionization process better.
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